The shipping industry of today strives to reduce harmful emissions, such as emissions originating from the combustion of fuel in the engine, in order to minimize the negative environmental impact and fulfill present and upcoming emission regulations.
One part in this is the reduction in sulphuric oxide (SOX) emissions from ships. Sulphuric oxides are created in the combustion of fuels containing sulphuric residues. The amount of sulphuric oxides in exhaust gas can be reduced by exhaust gas cleaning, e.g. by using scrubbers. The process of cleaning exhaust gas with the aid of the mentioned scrubbers produces polluted scrubber fluid.
Another object is the reductions in nitrogen oxides (NOX) emissions from marine engines. This can be done by implementing Exhaust Gas Recirculation (EGR), where part of the exhaust gas is recirculated to the combustion chamber of the engine. However, the amount of soot and particles in the exhaust gas needs to be decreased. It is therefore desirable to clean the exhaust gas, which can be done by using a scrubber. Also in this process polluted scrubber fluid is produced.
One problem is thus to improve the cleaning of the scrubber fluid. One further aspect of improving the cleaning of the scrubber fluid is to minimize the risk of pollutants being carried over from the scrubber fluid back into the exhaust gas where it may cause problems in downstream equipment such as coolers. A further problem is that particles in polluted scrubber fluid tend to adhere on process equipment and piping over time with the risk of a build-up of soot scaling resulting in malfunctioning process equipment, sensors, transmitters and the like. Equipment for cleaning scrubber fluid includes filter technology and centrifugal separators. However, equipment relying on filter technology has the drawback in the need for surveillance, service and replacement of filter components.
Further, during scrubbing of hot/warm exhaust gases by means of a wet scrubber, moisture in the exhaust gas may condensate into water, adding to the volume of scrubber fluid in the scrubber process. Further, various salts from the exhaust gas tend to be dissolved in the scrubber fluid in the scrubbing process. To reduce the risk of salt precipitates, the fluid may need to be diluted whereby the volume of scrubber fluid increases.
Fluid may thus be added to the scrubber fluid loop from the exhaust gas and/or due to deliberate addition of fluid to the system. To maintain the volume of scrubber fluid in the system, scrubber fluid has to be bled off from the scrubber process. However, the scrubber fluid may have to fulfill certain criteria, such as the IMO MEPC 184(59) criteria, to be discharged overboard.